Foamed compositions and methods of use in subterranean zones

ABSTRACT

The current invention provides improved methods and compositions for completing a well bore. In one aspect, the current invention provides a process for preparing a foamed well composition. The process utilizes air to foam the composition after the air has been treated to lower the oxygen content below that concentration necessary to support combustion. Additionally, the current invention provides a process for completing and/or treating a well bore using a foamed composition wherein the foam is generated with reduced oxygen content air. Finally, a preferred embodiment of the invention provides a foamed cement composition wherein the gaseous portion of the composition is air having a reduced oxygen content.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application is a Continuation-In-Part of application Ser.No. 10/386,822, filed Mar. 12, 2003, now pending.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to improved well completion methodsutilizing foamed cements and foamed well treatment fluids. Additionally,the present invention provides improved foamed cement and foamed welltreatment fluids and methods for preparing and using the same.

[0003] Foamed hydraulic cement compositions are often utilized incementing subterranean zones penetrated by well bores. For example,foamed cement compositions are used in primary well cementing operationswhereby strings of pipe such as casing and liners are cemented in wellbores. A primary cementing operation normally pumps a cement compositioninto the annular space between the walls of a well bore and the exteriorsurfaces of a pipe string disposed therein. The cement composition ispermitted to set in the annular space thereby forming an annular sheathof hardened substantially impermeable cement therein. Thus, the cementsheath physically supports and positions the pipe string in the wellbore and bonds the exterior surfaces of the pipe string to the walls ofthe well bore. In this manner, the cement precludes the undesirablemigration of fluids between zones or formations penetrated by the wellbore.

[0004] The geological nature of the formation will dictate the type ofcement composition appropriate for cementing operations. In order toprevent excessive hydrostatic pressure from unintentionally fracturingthe formation, certain formations will require lightweight cement. Toachieve the lower density of a lightweight cement, a foamed cementcomposition contains compressed gas which improves the ability of thecement composition to maintain the pressure necessary to prevent theflow of formation fluid into and through the cement composition duringthe transition time, i.e., the time during which the cement compositionchanges from a true fluid to a hard set mass. Foamed cement compositionsare also advantageous because they have low fluid loss properties due tothe two phases of the system. Therefore, the industry recognizes thebenefits of and frequently uses foamed cement and other foamed fluids insealing casing in subterranean wells.

[0005] Although similar to a conventional cementing operation, theprocess of foaming a cement or wellbore fluid requires additionalequipment not commonly associated with conventional cementingoperations. Typically, a hydraulic cement composition is foamed bycombining a mixture of foaming and foam stabilizing surfactants with thecement composition on the surface. Subsequently, as the cementcomposition is pumped into the well bore a gas, typically nitrogen, isinjected into the cement composition. This process allows the cementcomposition to have a downhole gas concentration, or foamed quality, offrom about 20% to about 80%, by volume of the cement compositiondepending on the downhole pressure and temperature. This processrequires the presence of nitrogen (liquid and/or gas) storage,vaporization, and pumping equipment at the well site. Normally equipmentof this nature is not used at well sites and may be unavailable ordifficult to transport to remote well sites. Clearly, the use ofnitrogen for foaming cement and wellbore fluids complicates and adds tothe overall burden of foam cementing a wellbore.

[0006] In the designing of the foam cement job, prediction software isutilized to estimate the amount of pressure, if any, required to controlthe expansion of the foamed fluids. If excessive expansion isencountered, the gas bubbles will become relatively large and coalescewhich will increase the permeability of the set cement. To accomplishprimary cementing with foam cement, it is desirable to have the wellheadequipped with annular pressure-containing devices. Whenpressure-containing devices are not feasible, the preferred practiceruns an unfoamed cement cap ahead of the foamed cement. The unfoamed“cap” interval should be tailored for each specific job. Typically, aninterval of 200-feet is considered the minimum length for the unfoamedcap.

[0007] For safety and clean-up ease, the return relief lines aretypically staked and chained to exit in an acceptable waste area, suchas a sump pit. Foamed cement under pressure will expand in volumeprolifically if released at atmospheric pressure. This foam is more of anuisance than a problem since it develops little strength and can bewashed away with a pressure hose.

[0008] In view of the problems inherent to foaming with nitrogen, itwould be desirable to provide improved foamed cements and foamed welltreatment fluids that do not require nitrogen to generate the foamedcement slurry. Further, considering the inherent risks associated withoxygen in the downhole environment, it would be desirable to provide afoamed cement wherein the foaming gas is air having a reduced oxygencontent.

SUMMARY OF THE INVENTION

[0009] The current invention provides methods and compositions suitablefor overcoming the problems identified with current foamed cementingpractices. In one aspect, the current invention provides a method offoaming cement with air. The method comprises the steps of preparing acement composition comprising hydraulic cement, sufficient water to forma slurry, and a mixture of foaming and foam stabilizing surfactants. Themethod also prepares compressed air with an oxygen content less than anamount necessary to support combustion of hydrocarbons. The compressedair with reduced oxygen content is used to foam the cement composition.

[0010] Additionally, the current invention provides a method of foamingcement with air. The improved method comprises the steps of preparing acement composition comprising hydraulic cement, sufficient water to forma slurry, and a mixture of foaming and foam stabilizing surfactantspresent in an amount sufficient to facilitate the formation andstabilization of foam. The method also prepares compressed air with anoxygen content less than an amount necessary to support combustion ofhydrocarbons by contacting the air with an oxygen scavenger prior to orafter compressing the air. In general, the order of compressing the airand contacting the air with an oxygen scavenger is not critical to thecurrent invention and may be reversed such that the oxygen content islowered by contact with an oxygen scavenger prior to or aftercompressing the air. The reduced oxygen content air is then used to foamthe cement composition.

[0011] The current invention further provides an improved method ofcementing a well bore penetrating a hydrocarbon producing subterraneanzone. The improved method comprises the steps of preparing a cementcomposition comprising hydraulic cement, sufficient water to form aslurry, and a mixture of foaming and foam stabilizing surfactants. Theimproved method also prepares compressed air with an oxygen content lessthan an amount necessary to support combustion of hydrocarbons presentin the well bore. The cement composition is foamed with the reducedoxygen content compressed air and placed into the subterranean zone.Following placement of the foamed cement, the cement is allowed to set.

[0012] In another embodiment the current invention provides an improvedmethod of cementing a well bore penetrating a hydrocarbon producingsubterranean zone. The improved method comprises the steps of preparinga cement composition comprising hydraulic cement, sufficient water toform a slurry, and a mixture of foaming and foam stabilizing surfactantspresent in an amount sufficient to facilitate the formation andstabilization of foam. The improved method also prepares compressed airwith an oxygen content less than an amount necessary to supportcombustion of hydrocarbons by contacting the air with an oxygenscavenger prior to or after compressing the air. Accordingly, the orderof compressing the air and contacting the air with an oxygen scavengeris not critical to the current invention and may be reversed such thatthe oxygen content is lowered by contact with an oxygen scavenger priorto or after compressing the air. The cement composition is foamed withthe reduced oxygen content compressed air and placed into thesubterranean zone. Following placement of the foamed cement, the cementis allowed to set into a solid mass.

[0013] The current invention also provides an improved foamed cementcomposition comprising a hydraulic cement, water, and air having anoxygen content less than an amount required to support combustion ofhydrocarbons. Typically the water is present in an amount sufficient toform a slurry of the hydraulic cement. Additionally, the foamed cementcomposition normally comprises from about 20% to about 80% reducedoxygen content air by volume.

[0014] In yet another embodiment, the current invention provides afoamed cement composition comprising a hydraulic cement, water; and, airhaving an oxygen content less than about 12.5% by volume. Typically thewater is present in an amount sufficient to form a slurry of thehydraulic cement. Additionally, the foamed cement composition normallycomprises from about 20% to about 80% reduced oxygen content air byvolume.

[0015] In yet another embodiment, the current invention provides foamedwell compositions having a well fluid, such as a drilling, completion orstimulation fluid, foamed with air having an oxygen content less than anamount required to support combustion of hydrocarbons and, morepreferably, air with an oxygen content less than about 12.5% by volume.

[0016] Other and further objects, features and advantages of the presentinvention will be readily apparent to those skilled in the art upon areading of the description of the preferred embodiments which follows.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] 1. Method of Preparing a Reduced Oxygen Content Foamed Cement

[0018] One aspect of the current invention provides a method forpreparing an improved foamed cement. The steps necessary to prepare afoamed cement are generally well known to those skilled in the art asdemonstrated by U.S. Pat. Nos. 6,500,252, 6,227,294, and 6,063,738, allof which are incorporated herein by reference.

[0019] The method of the current invention utilizes air with a reducedoxygen content as the gas phase. In the method of the current invention,a cement is prepared according to standard industry procedures. Thecement slurry is then foamed using air with an oxygen content lower thanthat necessary to support combustion of hydrocarbons. Preferably, theoxygen content is less than about 12.5% oxygen. More preferably, theoxygen content is less than about 5% oxygen by volume. The resultingfoamed cement is particularly suitable for carrying out primarycementing operations in wells as a result of the cement compositionsbeing lightweight, having low fluid loss, being compressible during theslurry's transition time, and having good thermal insulation properties.

[0020] The method of preparing air with lowered oxygen content comprisesthe steps of contacting the air with an oxygen scavenger and compressingthe air with a conventional compressor. In one embodiment, the aircontacts or passes through an oxygen scavenger such as sodiumthiosulfate available from Calabrian Corp. of Houston, Tex. Othercompounds suitable for removing oxygen from air include as sodiumsulfite, sodium bi-sulfite, pyrogallic acid, pyrogallol, catechal,sodium erthythrobate, ascorbic acid, amines, resorcinol, quinones, andhydroquinones. As the air contacts the oxygen scavenger, the compound(s)contained therein, absorb or adsorb oxygen from the air. Followingoxygen reduction, the air has an oxygen content of less than about 12.5%by volume, preferably, the oxygen content is less than about 5% byvolume. Following oxygen reduction the air is compressed using aconventional air compressor. Typically, the compressed air leaves thecompressor at a pressure in the range of about 100 KPa to about 14 MPa.

[0021] The order of compressing and reducing the oxygen content of theair is not critical to the current invention. Thus, it is within thescope of the current invention to first compress the air and thencontact the compressed air with an oxygen scavenger. Either method ofpreparing the reduced oxygen content compressed air should performsatisfactorily in the current invention.

[0022] A variety of hydraulic cements can be utilized in accordance withthe present invention including those comprised of calcium, aluminum,silicon, oxygen, and/or sulfur which set and harden by reaction withwater. Such hydraulic cements include Portland cements, pozzolaniccements, gypsum cements, high alumina cements, and silica cements.Portland cements or their equivalents are generally preferred for use inaccordance with the present invention when performing cementingoperations in subterranean zones penetrated by well bores. Portlandcements of the types defined and described in API Specification ForMaterials And Testing For Well Cements, API Specification 10, 5^(th)Edition, dated Jul. 1, 1990 of the American Petroleum Institute areparticularly suitable. Preferred API Portland cements include classes A,B, C, G and H, with API classes A, G and H being more preferred, andclasses G and H being the most preferred.

[0023] The water utilized to form the foamed cement compositions of thisinvention can be fresh water or salt water. The term “salt water” isused herein to mean unsaturated salt solutions and saturated saltsolutions including brines and seawater. The water is included in thefoamed cement compositions in an amount sufficient to slurry thehydraulic cement. Generally, the water is present in the foamed cementcompositions in an amount in the range of from about 30% to about 60% byweight of hydraulic cement therein.

[0024] The gas utilized for foaming the cement slurry is the reducedoxygen content air described above. The gas is present in an amountsufficient to foam the slurry, generally in an amount in the range offrom about 20% to about 80% by volume of the slurry.

[0025] Those skilled in the art are familiar with foaming and foamstabilizing surfactants suitable for use in the downhole environment. Apreferred mixture of such surfactants is described in U.S. Pat. No.5,897,699 issued to Chatterji et al. on Apr. 27, 1999, incorporatedherein by reference. The patent discloses an aqueous solution of amixture of an alpha-olefinic sulfonate and a cocoylamidopropyl betaine.

[0026] Another preferred foaming and foam stabilizing surfactant mixturefor use in accordance with the present invention is comprised of anethoxylated alcohol ether sulfate of the formulaH(CH₂)_(a)(OC₂H₄)_(b)OSO₃NH₄ ⁺ wherein “a” is an integer in the range offrom about 6 to about 10 and “b” is an integer in the range of fromabout 3 to about 10, an alkyl or alkene amidopropylbetaine having theformula R—CONHCH₂CH₂CH₂N⁺(CH₃)₂CH₂CO₂ ⁻ wherein R is a radical selectedfrom the group of decyl, cocoyl, lauryl, cetyl and oleyl and an alkyl oralkene amidopropyldimethylamineoxide having the formulaR′—CONHCH₂CH₂CH₂N⁺(CH₃)₂O⁻ wherein R′ is a radical selected from thegroup of decyl, cocoyl, lauryl, cetyl and oleyl.

[0027] The ethoxylated alcohol ether sulfate is generally present in theabove-described mixture in an amount in the range of from about 60 toabout 64 parts by weight. The alkyl or alkene amidopropylbetaine isgenerally present in the mixture in an amount in the range of from about30 to about 33 parts by weight and the alkyl or alkeneamidopropyldimethylamineoxide is generally present in the additive in anamount in the range of from about 3 to about 10 parts by weight.

[0028] The most preferred foaming and foam stabilizing surfactantmixture of the type described above for use in accordance with thisinvention is comprised of an ethoxylated alcohol ether sulfate wherein“a” in the formula set forth above is an integer in the range of fromabout 6 to about 10 and the ethoxylated alcohol ether sulfate is presentin the surfactant mixture in an amount of about 63.3 parts by weight;the alkyl or alkene amidopropyl-betaine is cocoylamidopropylbetaine andis present in the mixture in an amount of about 31.7 parts by weight andthe alkyl or alkene amidopropyldimethylamineoxide iscocoylamidopropyldimethylamineoxide and is present in an amount of about5 parts by weight.

[0029] The foaming and foam stabilizing surfactant mixture is generallyincluded in the foamed cement composition of this invention in an amountin the range of from about 0.5% to about 5% by volume of water in thecement slurry, preferably in an amount of from about 1% to about 2.5%.

[0030] As will be understood by those skilled in the art, the foamedwell cement compositions of this invention can include a variety ofconventional additives for improving or changing the properties of thefoamed cement compositions. Examples of such additives include, but arenot limited to, set retarding agents, fluid loss control agents, setaccelerating agents and formation conditioning agents.

[0031] Set retarding agents are included in the foamed cementcompositions when it is necessary to extend the time in which the foamedcement compositions can be pumped so that they will not set prior tobeing placed at a desired location in a well. Examples of set retardingagents which can be used include, but are not limited to,lignosulfonates such as calcium and sodium lignosulfonate, organic acidssuch as tartaric acid and gluconic acid, copolymers of acrylic acid,maleic acid and others. The proper amount of set retarding agentrequired for particular conditions can be determined by conducting a“thickening time test” for the particular retarder and foamed cementcomposition. Such tests are described in the API Recommend Practice 10Bmentioned above. A suitable set retarder for use in accordance with thepresent invention is a copolymer or copolymer salt of2-acrylamido-2-methylpropane sulfonic acid and acrylic acid. Thecopolymer comprises from about 60 to about 90 mole percent2-acrylamido-2-methylpropane sulfonic acid with the balance comprisingacrylic acid, and the copolymer or salt thereof preferably has anaverage molecular weight below about 5,000. The most preferred retardantis described in U.S. Pat. No. 6,227,294, which is incorporated herein byreference. When used, a set retarder is included in the foamed cementcompositions of this invention in amounts ranging from about 0.1% toabout 2% by weight of hydraulic cement in the compositions.

[0032] Examples of suitable set accelerating agents include, but are notlimited to, calcium chloride, zinc formate and triethanolamine, andexamples of formation conditioning agents include, but are not limitedto, potassium chloride and sodium chloride.

[0033] The foamed cement slurries of this invention may be prepared inaccordance with any of the mixing techniques utilized in the art. In onepreferred method, a quantity of water is introduced into a cementblender followed by the hydraulic cement utilized. A preferred cementcomposition suitable for foaming comprises Portland cement and a mixtureof foaming and foam stabilizing surfactants. The mixture of foaming andfoam stabilizing surfactants being present in the cement composition inan amount ranging from about 1% to about 5% by volume of the water inthe composition. The mixture is agitated for a sufficient period of timeto form a pumpable non-foamed slurry. Other liquid additives utilized,if any, are preferably added to the water prior to when the hydrauliccement is mixed therewith and other dry solids, if any, are normallyadded to the water and cement prior to mixing.

[0034] Following formation of the non-foamed slurry, the reduced oxygencontent air is injected into the slurry to form a foamed cement. Aspreviously noted, the injected air should have an oxygen content ofabout 12.5% by volume or less. Preferably, the oxygen content is lessthan about 5% by volume.

[0035] 2. Method of Cementing with a Reduced Oxygen Content Cement

[0036] Cementing operations are carried out in oil and gas wells for avariety of reasons. The most common operations are performed to secure acasing within the well bore and to isolate non-producing or waterproducing zones from hydrocarbon producing zones. As noted above,cementing processes using foamed cement require additional steps topreclude coalescence of the gas cells within the foamed cement.

[0037] When using foamed cement for the primary cementing operation, thewellhead is preferably equipped with an annular pressure-containingdevice. If a pressure-containing device is unavailable, then an unfoamedcement cap is injected ahead of the foamed cement. The unfoamed capinterval should be tailored for each specific job. Typically, a 200-footinterval is considered the minimum length for the unfoamed cap.

[0038] Prior to the current invention, oxygen-containing gases such asair were not suitable for foaming a cement. Due to the presence ofhydrocarbons within the well bore, the introduction of air into thewellbore would likely create a combustible gas in the well bore. Ingeneral, the possibility of an explosion exists when natural gas andother hydrocarbons associated with petroleum are exposed to an oxygenconcentration of greater than about 12.5% by volume. The concentrationof oxygen necessary to support combustion will decrease as temperatureand pressure increases. Additionally, once the oxygen/hydrocarbonmixture reaches critical mass, the chance of an explosion increasesexponentially with increasing pressure. Therefore, to reduce the risk ofan uncontrolled downhole explosion, current foaming operations aretypically performed with nitrogen. However, as mentioned above, nitrogeninjection requires the use of equipment not commonly found at the wellbore site.

[0039] Accordingly, the current invention provides an improved cementingmethod wherein foaming operations are carried out by injection ofreduced oxygen content air into the desired cement composition. Themethod of preparing air with lowered oxygen content comprises the stepsof contacting the air with an oxygen scavenger and compressing the airwith a conventional compressor. In one embodiment, the air contacts orpasses through an oxygen scavenger such as sodium thiosulfate availablefrom Calabrian Corp. of Houston, Tex. Other compounds suitable forremoving oxygen from air include as sodium sulfite, sodium bi-sulfite,pyrogallic acid, pyrogallol, catechal, sodium erthythrobate, ascorbicacid, amines, resorcinol, quinones, and hydroquinones. As the aircontacts the oxygen scavenger, the compound(s) contained therein, absorbor adsorb oxygen from the air. After contacting the oxygen scavenger,the oxygen content of the air has been lowered sufficiently to precludecombustion of hydrocarbons found in the well bore. Preferably, theoxygen content is less than about 12.5% by volume. More preferably, theoxygen content is less than about 5% by volume. As noted above, loweringthe oxygen concentration to about 12.5% or less by volume will reducingthe likelihood of an uncontrolled explosion in the downhole environment.Following oxygen reduction the air is compressed using a conventionalair compressor. Typically, the compressed air leaves the compressor at apressure in the range of about 100 KPa to about 14 MPa.

[0040] As indicated above, the order of compressing and reducing theoxygen content of the air is not critical to the current invention.Thus, it is within the scope of the current invention to first compressthe air and then contact the compressed air with an oxygen scavenger.Either method of preparing the reduced oxygen content compressed airshould perform satisfactorily in the current invention.

[0041] As known to those skilled in the art, oxygen scavengers arecompounds capable of absorbing or adsorbing oxygen from air. Forexample, SPE paper number 28978, “Effects of Oxygen on FracturingFluids,” by Walker et al., 1995, demonstrates that one mole of sodiumthiosulfate is capable of consuming 2 moles of oxygen. Likewise a moleof sodium sulfite is will consume one mole of oxygen. Other commonlyused oxygen scavenging compounds include sodium thiosulfate, sodiumsulfite, sodium bi-sulfite, pyrogallic acid, pyrogallol, catechal,sodium erthythrobate, ascorbic acid, amines, resorcinol, quinones andhydroquinones. A preferred compound is sodium thiosulfate available fromCalabrian Corp. of Houston, Tex.

[0042] Following preparation of the reduced oxygen content compressedair, the air is injected into the cement, according to standardoperating procedures known to those skilled in the art, at a ratesufficient to produce a foamed cement. One preferred method of cementingwith reduced oxygen content foamed cement comprises the steps of: (a)preparing a non-foamed cement slurry comprised of Portland cement,sufficient water to produce a slurry and a mixture of foaming and foamstabilizing surfactants, the mixture being present in the cementcomposition in an amount ranging from about 1% to about 5% by volume ofthe water in the composition; (b) preparing reduced oxygen contentcompressed air having an oxygen content in the compressed air of lessthan about 12.5% by volume or less; (c) foaming the cement compositionby injecting the reduced oxygen air into the cement composition; (d)placing the resulting foamed cement at the desired downhole location;and, (e) allowing the foamed cement composition to set into a solid masstherein. Other liquid additives utilized, if any, are preferably addedto the water prior to when the hydraulic cement is mixed therewith andother dry solids, if any, are normally added to the water and cementprior to mixing.

[0043] 3. Foamed Cement Composition Containing Reduced Oxygen ContentAir

[0044] The current invention also provides a novel foamed cementcomposition. The foamed cement composition of the current inventioneliminates the need for liquid nitrogen storage or other cryogenicequipment production at the well bore. Briefly stated, the foamed cementcomposition of the current invention comprises hydraulic cement,sufficient water to produce a slurry, a mixture of foaming and foamstabilizing surfactants and sufficient reduced oxygen content air tofoam the slurry. Additionally, as known to those skilled in the artother performance enhancing additives such as, but not limited to, setretarding agents, fluid loss control agents, set accelerating agents andformation conditioning agents may be included in the foamed cementcomposition.

[0045] Preferred cements include Portland cements, pozzolan cements,gypsum cements, high alumina content cements, silica cements and highalkalinity cements. Portland cements or their equivalents are generallypreferred for use in accordance with the present invention whenperforming cementing operations in subterranean zones penetrated by wellbores. Portland cements of the types defined and described in APISpecification For Materials And Testing For Well Cements, APISpecification 10, 5^(th) Edition, dated Jul. 1, 1990 of the AmericanPetroleum Institute are particularly suitable. Preferred API Portlandcements include classes A, B, C, G and H, with API classes A, G and Hbeing more preferred, and class G and H being the most preferred.

[0046] The water in the foamed cement composition may be fresh water orsalt water, as defined above. Preferably, the concentration of water inthe foamed cement is in the range of about 30% to about 60% by weight ofthe hydraulic cement therein.

[0047] The gas contained within the foamed cement is reduced oxygencontent air. Typically, from about 20% to about 80% of the volume of thefoamed cement is the reduced oxygen content air. Preferably, from about20% to about 60% by volume of the foamed cement is the reduced oxygencontent air.

[0048] Finally, the foaming and foam stabilizing surfactant mixturefound in the foamed cement composition generally corresponds to about0.5% to about 5% by volume of the water found in the cement slurry. Morepreferably the foaming and foam stabilizing surfactant mixture in thefoamed cement composition corresponds to about 1% to about 2.5% byvolume of the water found in the cement slurry.

[0049] Thus, a particularly preferred foamed cement composition whichupon setting has high strength, resiliency, ductility and toughness iscomprised of Portland cement, a mixture of foaming and foam stabilizingsurfactants, the mixture being present in the cement composition in anamount ranging from about 0.5% to about 5% by volume of the water in thecomposition, and sufficient water to slurry the cement. Additionally,the preferred foamed cement composition comprises sufficient reducedoxygen content air to foam the slurry. At a minimum, the reduced oxygencontent air has an oxygen content lower than an amount necessary tosupport combustion of hydrocarbons. Preferably, the reduced oxygencontent compressed air has less than about 12.5% oxygen by volume. Morepreferably the reduced oxygen content air contains less than about 5%oxygen by volume. Preferably, the foamed cement composition willcomprise from about 20% to about 60% by volume reduced oxygen contentair.

[0050] While the preferred embodiments described herein relate to foamedcement compositions, it is understood that any foamed well treatmentfluids such as drilling, completion and stimulation fluids including,but not limited to, drilling muds, well cleanup fluids, workover fluids,spacer fluids, gravel pack fluids, acidizing fluids, fracturing fluidsand the like can be prepared using compressed air with an oxygen contentless than an amount necessary to support combustion of hydrocarbonspresent in the well bore. Accordingly, improved methods of the presentinvention comprise the steps of preparing a foamed well treatment fluidusing compressed air having a reduced oxygen content, as previouslydescribed herein, and placing the foamed fluid in a subterraneanformation. Examples of such foamed well treatment fluids are describedin U.S. Pat. Nos. 6,460,632; 6,454,008; 5,851,960; 5,716,910; 5,358,047;4,453,596 and 4,436,156; and U.S. patent application Ser. No. 10/393,965filed Mar. 21, 2003 assigned to the assignee of the present invention,all of which are incorporated herein by reference.

[0051] Preferred methods of foaming a well treatment fluid comprise thesteps of providing a foamable well treatment fluid; providing compressedair with an oxygen content less than an amount necessary to supportcombustion of hydrocarbons in an amount sufficient to foam the fluid;and foaming the fluid with the reduced oxygen content compressed air.Additional steps include placing the resulting foamed composition into asubterranean zone; drilling, completing and/or stimulating asubterranean formation using the foamed treatment fluid and producing afluid, e.g., a hydrocarbon fluid such as oil or gas, from thesubterranean formation.

[0052] Other embodiments of the current invention will be apparent tothose skilled in the art from a consideration of this specification orpractice of the invention disclosed herein. However, the foregoingspecification is considered merely exemplary of the current inventionwith the true scope and spirit of the invention being indicated by thefollowing claims.

What is claimed is:
 1. A method of foaming a well fluid comprising thesteps of: providing a foamable well fluid; providing compressed air withan oxygen content less than an amount necessary to support combustion ofhydrocarbons; and foaming the fluid with the reduced oxygen contentcompressed air.
 2. The method of claim 1 wherein the compressed air hasless than about 12.5% oxygen content by volume.
 3. The method of claim 1wherein the compressed air has less than about 5% oxygen content byvolume.
 4. The method of claim 1 wherein the step of preparing thecompressed air comprises contacting the air with an oxygen scavengerprior to or after compressing the air.
 5. The method of claim 4 whereinthe oxygen scavenger is selected from the group consisting of sodiumthiosulfate, sodium sulfite, sodium bi-sulfite, pyrogallic acid,pyrogallol, catechal, sodium erthythrobate, ascorbic acid, amines,resorcinol, quinones and hydroquinones and mixtures thereof.
 7. Themethod of claim 1 wherein the foamed fluid comprises from about 20% toabout 80% reduced oxygen content air by volume.
 8. The method of claim 1wherein the foamed fluid comprises from about 20% to about 60% reducedoxygen content air by volume.
 9. The method of claim 1 wherein the fluidcomprises a mixture of foaming and foam stabilization surfactantspresent in the range of from about 0.5% to about 5% by volume of waterin the fluid.
 10. The method of claim 9 wherein the mixture of foamingand foam stabilization surfactants are present in the range of fromabout 1% to about 2.5% by volume of water in the fluid.
 11. The methodof claim 1 wherein the fluid comprises a mixture of foaming and foamstabilization surfactants comprising an alpha-olefinic sulfonate and acocoylamidopropyl betaine.
 12. The method of claim 1 wherein the fluidcomprises a mixture of foaming and foam stabilization surfactantscomprising an ethoxylated alcohol ether sulfate of the formulaH(CH₂)_(a)(OC₂H₄)_(b)OSO₃NH₄ ⁺ wherein “a” is an integer in the range offrom about 6 to about 10 and “b” is an integer in the range of fromabout 3 to about 10, an alkyl or alkene amidopropylbetaine having theformula R—CONHCH₂CH₂CH₂N⁺(CH₃)₂CH₂CO₂ ⁻ wherein R is a radical selectedfrom the group consisting of decyl, cocoyl, lauryl, cetyl and oleyl andan alkyl or alkene amidopropyldimethylamineoxide having the formulaR′—CONHCH₂CH₂CH₂N⁺(CH₃)₂O⁻ wherein R′ is a radical selected from thegroup consisting of decyl, cocoyl, lauryl, cetyl and oleyl.
 13. Themethod of claim 12 wherein the ethoxylated alcohol ether sulfate ispresent in an amount ranging from about 60 to about 64 parts by weight,the alkyl or alkene amidopropylbetaine is present in an amount rangingfrom about 30 to about 33 parts by weight and the alkyl or alkeneamidopropyldimethylamineoxide is present in an amount ranging from about3 to about 10 parts by weight of the mixture of foaming and foamstabilization surfactants.
 14. The method of claim 1 wherein the wellfluid is selected from the group consisting of drilling fluids,completion fluids, and stimulation fluids.
 15. The method of claim 1wherein the well fluid is selected from the group consisting of drillingmuds, well cleanup fluids, workover fluids, spacer fluids, gravel packfluids, acidizing fluids, and fracturing fluids.
 16. The method of claim1 further comprising the step of placing the resulting foamed fluid intoa subterranean zone.
 17. The method of claim 1 further comprising thestep of drilling, completing and/or stimulating a subterranean formationusing the foamed fluid.
 18. The method of claim 1 further comprising thestep of producing a fluid from the subterranean formation.
 19. Themethod of claim 18 wherein the fluid produced from the formation is oiland/or gas.
 20. A foamed well composition comprising: a well fluid; andair having an oxygen content less than an amount required to supportcombustion of hydrocarbons present in an amount sufficient to foam thefluid.
 21. The composition of claim 20 wherein the air has less thanabout 12.5% oxygen content by volume.
 22. The composition of claim 20wherein the air has less than about 5% oxygen content by volume.
 23. Thecomposition of claim 20 wherein the air is prepared using an oxygenscavenger.
 24. The composition of claim 23 wherein the oxygen scavengeris selected from the group consisting of sodium thiosulfate, sodiumsulfite, sodium bi-sulfite, pyrogallic acid, pyrogallol, catechal,sodium erthythrobate, ascorbic acid, amines, resorcinol, quinones andhydroquinones and mixtures thereof.
 25. The composition of claim 20wherein the foamed fluid comprises from about 20% to about 80% reducedoxygen content air by volume.
 26. The composition of claim 20 whereinthe foamed fluid comprises from about 20% to about 60% reduced oxygencontent air by volume.
 27. The composition of claim 20 wherein the fluidcomprises a mixture of foaming and foam stabilization surfactantspresent in the range of from about 0.5% to about 5% by volume of waterin the fluid.
 28. The composition of claim 27 wherein the mixture offoaming and foam stabilization surfactants are present in the range offrom about 1% to about 2.5% by volume of water in the fluid.
 29. Thecomposition of claim 20 wherein the fluid comprises a mixture of foamingand foam stabilization surfactants comprising an alpha-olefinicsulfonate and a cocoylamidopropyl betaine.
 30. The composition of claim20 wherein the fluid comprises a mixture of foaming and foamstabilization surfactants comprising an ethoxylated alcohol ethersulfate of the formula H(CH₂)_(a)(OC₂H₄)_(b)OSO₃NH₄ ⁺ wherein “a” is aninteger in the range of from about 6 to about 10 and “b” is an integerin the range of from about 3 to about 10, an alkyl or alkeneamidopropylbetaine having the formula R—CONHCH₂CH₂CH₂N⁺(CH₃)₂CH₂CO₂ ⁻wherein R is a radical selected from the group consisting of decyl,cocoyl, lauryl, cetyl and oleyl and an alkyl or alkeneamidopropyldimethylamineoxide having the formulaR′—CONHCH₂CH₂CH₂N⁺(CH₃)₂O⁻ wherein R′ is a radical selected from thegroup consisting of decyl, cocoyl, lauryl, cetyl and oleyl.
 31. Themethod of claim 30 wherein the ethoxylated alcohol ether sulfate ispresent in an amount ranging from about 60 to about 64 parts by weight,the alkyl or alkene amidopropylbetaine is present in an amount rangingfrom about 30 to about 33 parts by weight and the alkyl or alkeneamidopropyldimethylamineoxide is present in an amount ranging from about3 to about 10 parts by weight of the mixture of foaming and foamstabilization surfactants.
 32. The composition of claim 20 wherein thewell fluid is selected from the group consisting of drilling fluids,completion fluids, and stimulation fluids.
 33. The composition of claim20 wherein the well fluid is selected from the group consisting ofdrilling muds, well cleanup fluids, workover fluids, spacer fluids,gravel pack fluids, acidizing fluids, and fracturing fluids.
 34. Afoamed well composition comprising: a well fluid selected from the groupconsisting of drilling fluids, completion fluids, and stimulationfluids; and air having less than about 12.5% oxygen content by volumepresent in an amount sufficient to foam the fluid.
 35. The compositionof claim 34 wherein the air is prepared using an oxygen scavenger. 36.The composition of claim 35 wherein the oxygen scavenger is selectedfrom the group consisting of sodium thiosulfate, sodium sulfite, sodiumbi-sulfite, pyrogallic acid, pyrogallol, catechal, sodium erthythrobate,ascorbic acid, amines, resorcinol, quinones and hydroquinones andmixtures thereof.
 37. The composition of claim 34 wherein the air ispresent in an amount from about 20% to about 80% by volume.
 38. Thecomposition of claim 34 wherein the fluid comprises a mixture foamingand foam stabilization surfactants.
 39. The composition of claim 38wherein the foaming and foam stabilization surfactants are present inthe range of from about 0.5% to about 5% by volume of water in thefluid.
 40. The composition of claim 38 wherein the mixture of foamingand foam stabilization surfactants comprises an alpha-olefinic sulfonateand a cocoylamidopropyl betaine.
 41. The composition of claim 38 whereinthe mixture of foaming and foam stabilization surfactants comprises anethoxylated alcohol ether sulfate of the formulaH(CH₂)_(a)(OC₂H₄)_(b)OSO₃NH₄ ⁺ wherein “a” is an integer in the range offrom about 6 to about 10 and “b” is an integer in the range of fromabout 3 to about 10, an alkyl or alkene amidopropylbetaine having theformula R—CONHCH₂CH₂CH₂N⁺(CH₃)₂CH₂CO₂ ⁻ wherein R is a radical selectedfrom the group consisting of decyl, cocoyl, lauryl, cetyl and oleyl andan alkyl or alkene amidopropyldimethylamineoxide having the formulaR′—CONHCH₂CH₂CH₂N⁺(CH₃)₂O⁻ wherein R′ is a radical selected from thegroup consisting of decyl, cocoyl, lauryl, cetyl and oleyl.
 42. Thecomposition of claim 41 wherein the ethoxylated alcohol ether sulfate ispresent in an amount ranging from about 60 to about 64 parts by weight,the alkyl or alkene amidopropylbetaine is present in an amount rangingfrom about 30 to about 33 parts by weight and the alkyl or alkeneamidopropyldimethylamineoxide is present in an amount ranging from about3 to about 10 parts by weight of the mixture of foaming and foamstabilization surfactants.
 43. The composition of claim 34 wherein thewell fluid is selected from the group consisting of drilling muds, wellcleanup fluids, workover fluids, spacer fluids, gravel pack fluids,acidizing fluids, and fracturing fluids.